Here's a way to infuriate people by getting them to attempt the impossible: ask them, as BBC6 recently did, to choose the worst cover version of all time. Why is it impossible? There are too many candidates. Listeners eventually voted for Madonna's version of American Pie, but it could have been any one of dozens: Duran Duran's startling attempt at Public Enemy's 911 is a Joke, Gareth Gates' rendition of Suspicious Minds, or the enervated Sugababes/Girls Aloud collaboration for Comic Relief, Walk this Way, which reached No 1 last month. All provoke one question: what were they thinking?

Now is the right moment to be asking, because cover versions are in the spotlight this spring. Bryan Ferry recently served up Dylanesque, in which the tweedy squire took on 11 of you-know-who's big ones, while this month brings Patti Smith's interpretations of other people's tunes, Twelve. The same week as Smith's album comes out, hotshot producer Mark Ronson releases Version, featuring his rearrangements of famous songs. That's not all. Placebo, too, are finishing a covers album. Even Scarlett Johansson feels the need to weigh in with a record called Scarlett Sings Tom Waits.

The appearance of this little glut is probably coincidental, but together they make the point that covers can have as much legitimacy as original material. The assumption that it's more credible for artists to record only self-penned songs is challenged by, among others, Ferry's late-night take on Dylan's Gates of Eden and Amy Winehouse's raunchified version of the Zutons' Valerie, which appears on the Mark Ronson album.

It takes considerable chutzpah for Pop Star A to decide that what the world has been waiting for is his/her interpretation of Pop Star B's finest moments, yet the success of Dylanesque - Ferry's first top 5 album in 14 years - justifies the gamble. Dylanesque is a lesson in how to bend a cover to suit the coverer's style. Refusing to be intimidated by the Zimmerman legacy, Ferry imprints his own dinner-jacketed identity on the songs. Guns N' Roses did the same when they took on Dylan's Knockin' on Heaven's Door, building it into an arena anthem that only vaguely resembled the original, while Jimi Hendrix made All Along the Watchtower utterly his own, with a scorched reworking that still fools people into believing he, not Dylan, wrote it.

It's not that Dylan is simply easy to cover, but Ferry, GN'R and Hendrix did it their own way, which is the primary rule for making superior covers.

Ronson, a New Yorker, followed the same rule when putting together Version. "You want to make them different, and truly change the arrangement. Those are the kind of covers that take on a life of their own." To make Version different, he employed crunchy 70s funk rhythms, which completely change the character of the tracks covered. His matching up of, for instance, the late Ol' Dirty Bastard and the Britney Spears hit Toxic is every bit the weirdfest you'd expect - in the right way, luckily. Ditto his idea of having Lily Allen tootle along to the Kaiser Chiefs' Oh My God.

"I've always been drawn to the 60s and 70s," he explains. "Arrangers of the day, like Quincy Jones and Henry Mancini, would put out a record every year of them playing the hits of the day, and I see myself as an extension of that."

That kind of fruitful rummaging around in a song's innards ought to shame acts who use covers as a lazy way of creating ballast on an album, or of scoring a cheap hit single. Even worse, perhaps, are those conceived in the name of sincere homage by artists who simply aren't equal to it.

Ronson tuts a bit. "Normally, it's people from a similar genre covering a similar song, and it's not that interesting. They toss it out, like Girls Aloud covering a Tiffany record [I Think We're Alone Now, itself a cover of Tommy James's 1967 original] - they're going to sound just as bubblegum as Tiffany."

But definitive versions can also come from acts generically similar to the one they're covering. It wasn't exactly a stretch for Erasure, then a highly successful synth-pop duo, to record four Abba songs and release them as the Abbaesque EP in 1992. "It was something I just had to do," says singer Andy Bell. "I just loved the passion they had in their songs, and wanted to sing them live." The result: a No 1 record for Erasure, and a new lease of life for Abba, who capitalised on it by putting out a greatest-hits album that spent 352 weeks in the chart. "Abba sent us a limited edition with all their hits on it, but we didn't hear anything else from them," Bell says philosophically.

Bell's adoration of Abba illustrates the other main criterion for successfully reworking a song: love it as you would your own material. "I listened to [the Smiths'] Stop Me if You Think You've Heard This One Before seven billion times when I was growing up," says Ronson, who asked Australian soul singer Daniel Merriweather to record it for Version. That hasn't stopped a few Smiths nuts, who consider any cover to be sacrilege, from "calling for blood", but he's unrepentant. "I could be the town pariah, but you can hear the dedication to the original, every little detailed thing, so I don't care what Smiths fans think."

Done the right way, a cover can get a career off the ground, though what happens afterwards depends on talent and, to a large degree, luck. Imagine the Futureheads' excitement when, after three unsuccessful original singles, a striking reading of Kate Bush's Hounds of Love took them into the top 10 two years ago. Then imagine their dismay when that song overshadowed all their subsequent releases, which stalled in the lower regions of the chart. Last year, they were dropped by their label.

"I would have preferred one of our own to be our biggest hit, [but] that's one of our anthems," says Barry Hyde, whose staccato yelp gave their version its kapow. "We'd been doing Hounds of Love for years, because covers are really handy for new bands, when you only have about four original songs in your set. We loved the song and we loved Kate Bush, and that's why it turned out as a good cover."

Similarly, Soft Cell recorded Tainted Love - a Northern Soul standard by Texas singer Gloria Jones, first recorded in 1964 - because keyboard player Dave Ball had danced to it as a clubgoing Leeds teenager. As with the Futureheads and Hounds of Love, Ball and partner Marc Almond changed the song beyond recognition. Its selling point was what Ball calls "the bleepy bits" - the result of "us messing around with syndrums. It was actually Marc who came up with it." It was 1981, synth-pop was all the rage and their chilly, bleeping remake of a hot-blooded R&B song shot straight to the top of the singles chart. "We just wanted to get into the indie chart. We'd have been happy with a Top 20 indie hit," Ball recalls. The single went to No 1 in 17 countries, sold a million copies in Britain and set up Soft Cell as one of the era's biggest pop groups.

Gloria Jones, who was better known in this country for having been Marc Bolan's girlfriend than for her singing, considers Soft Cell's remake to be the definitive version. "Soft Cell's rendition took Tainted Love to a greater level," Jones says via email from Sierra Leone, where she now lives. "I have total respect for the group. It was a northern soul hit for years, but they actually took it to No 1 over the world, and I loved it." The Futureheads received a similar pat on the back from Kate Bush, who "left us a message, saying she loved our version". Hyde ruefully adds that they were out when she phoned.

Ball has experience of being both coverer and coveree, with his own Soft Cell tunes appearing on albums by, among others, Nine Inch Nails and David Gray. So what does it feel like to hear your song played by someone else?

"I'm flattered at the idea that anyone would cover a song of mine, no matter who. What was interesting about what David [Gray] did with Say Hello, Wave Goodbye was that he integrated a bit of Van Morrison into it." He chuckles richly. "It sold 6 million. The money was nice."

Under the covers with AC/DC

Everyone knows AC/DC: neanderthal,sexist heavy-rock pigs from Australia.But they've spawned some of the mostimaginative - and one of the worst- cover versions of recent years.

Mark Kozelek is best known as thelugubrious singer of US miserablistsRed House Painters. But in 2001,he released a solo album composedentirely of AC/DC covers,What's Next to the Moon. Hepicked mainly from the band'searly albums, packed with songsabout struggle and despair,and recontextualised them ascountry-folk laments. EvenAC/DC's ill-advised forayinto disco-metal, 1979's LoveHungry Man, became a thing ofmaudlin beauty.

Norway's Susanna and theMagical Orchestra pulled asimilar trick with their readingof It's a Long Way to the Top (If YouWanna Rock'n'Roll) on last year'sMelody Mountain album, transformingan up tempo rocker into somethingfunereal, with a chorus like a stainedglasswindow's depiction of a shaft oflight through the clouds.

As for getting it badly wrong,you can consult the works ofHayseed Dixie (novelty bluegrass:horrible). Or take a lookat this. Yes,that really is Celine Dion tryingto tackle the 1980 raunchathonYou Shook Me All Night Long.Yes, she really does try to looksexy while singing "Knockingme out with those Americanthighs." And just when youthink it can't get any worse ...up pops Anastacia to duet. Thehorror, the horror. Michael Hann